Micro Electro-Mechanical Systems (MEMS) for use in optical switching applications typically contain optical mirrors that are controllable electronically. The optical mirrors are typically micro-machined from a silicon wafer and coated with various materials to produce a reflective mirror surface. The mirror structure is typically bonded onto a substrate, and the resulting structure is typically packaged within a glass-covered package. The glass allows light to pass to and from the optical mirrors.
A technique for testing aluminum electrostatic actuators is described in “A High-Resolution Laser-Based Deflection Measurement System for Characterizing Aluminum Electrostatic Actuators,” Proceedings of Transducers 1995, Stockholm, Sweden, pp. 308–311, which is hereby incorporated herein by reference in its entirety. Specifically, a laser beam is directed through an attenutator, a beam splitter and a lens onto an actuator. The reflected beam passes back through the lens and is directed by the beam splitter onto two photodiodes. Changes in the position of the actuator are detected as changes in the amount of illumination of the two photodiodes.
U.S. Pat. No. 6,052,197, “Apparatus for Wafer Level Testing of a Micromachined Device,” Apr. 18, 2000, which is hereby incorporated herein by reference, describes a technique for wafer level testing of a micromachined device. A control station is coupled to an electro-optical assembly that has been designed for the purpose of testing mirrors. Three standard probes are coupled to the electro-optic probe assembly to provide electrical connections to a particular mirror of a wafer under test. Optical components are coupled to the electro-optic probe to deliver laser light to a deflectable plate portion of the mirror. Displacement of the reflected laser light spot is detected as the mirror plate is vectored and this displacement is compare to specifications such that the mirror under test can be either accepted or rejected.
As discussed in U.S. Pat. No. 6,052,197, the technique for testing aluminum electrostatic actuators can be used to test optical mirrors in MEMS devices.